EP0978959A1 - Management method allowing signalling informations reception in a radio terminal communicating in a TDMA mode with a fixed station - Google Patents

Abstract

Changing the channel order gives more time to set the channel frequency, so that only one, rather than two local oscillators are needed for setting.

Description

The field of the invention is that of data transmission digital between a terminal, possibly mobile, and fixed stations making part of a cellular communication network. More specifically, this The invention relates to a method enabling a terminal to communicate in mode. TDMA with a fixed station to receive signaling information from this fixed station and also other fixed stations in the cellular network.

We will place ourselves in the rest of this description in the context of a terminal able to communicate with fixed stations forming a small cellular network private. The fixed stations are for example distributed in offices of a building, connected to the public network via a PABX, and the user of the terminal must be able to communicate without interruption with a third party while traveling in the building. Communication transfer procedures between stations fixed or even "handover" ensure this continuity of communication.

FIG. 1 represents a multiframe transmitted in such a network cellular.

The multiframe in Figure 1, generally referenced by 10, has 52 consecutive frames, noted T0 to T51. Each frame comprises for example 8 time intervals IT0 to IT7. Guard times are provided between frames and, after frame T51, a new multiframe appears.

Frames T0 to T24 and T26 to T50 are traffic frames intended for carry only traffic data between terminals and a fixed station given. This traffic data communication is carried out in the ascending and descending, a given terminal at which a time interval is assigned for the duration of a call receiving traffic data during one time interval and transmitting traffic data during another time interval, these time intervals may or may not be part of the same frame.

The T25 and T51 frames are signaling frames reserved for the reception, at each terminal, of signaling information broadcast by the different fixed stations of the network. This signaling information has in particular to allow terminals to decide whether it is necessary to carry out handover procedures, in order to continue their communications in progress with fixed stations better received. This decision can for example be performed on the basis of a power criterion received from this information signage. Each fixed station in the network is therefore allocated for the duration of the terminal communication, a time interval in frames T25 and T51. The fixed stations are synchronized with each other and with each terminal being communication must receive all signaling information transmitted by the different fixed stations.

Figure 2 shows in more detail the frames T24 and T25 of the multiframe of figure 1.

As previously indicated, the time intervals IT0 to IT7 of the T24 traffic frame carries traffic data, in the uplink and / or downlink, and the T25 signaling frame is reserved for reception signaling information transmitted by the various fixed stations of the cellular network. This signaling information is preferably, for reasons of simplicity, transmitted on the same frequency.

The problem with such a communication network is that not only must be able to transmit and receive traffic data in the time intervals allocated to them, but also being able receive, if not all the multiframes at least from time to time, the signaling data broadcast by fixed stations, in order to be able to request handover procedures. However, this requires local oscillators at the level of terminals that can quickly change frequency. For example, the terminal to which the IT7 time interval has been allocated must be able, within a period corresponding to the guard time planned between the frames, change its frequency transmission or reception to properly receive information from signaling carried in the IT0 time interval of the T25 frame. This problem actually arises when the local oscillator is not enough fast to go from the frequency of transmission or reception of data from traffic at the frequency of reception of signaling information. Therefore, if the frequency change had to last more than one time interval (in considering zero guard time), we would have the same problem in terms of terminal to which the IT6 time interval is allocated.

The same problem arises when switching from the frequency of reception of signaling information in the T25 frame to that of transmission and / or reception of traffic data in the T26 frame. Local oscillators able to change frequency as quickly (in times less than 777 microseconds) do not exist on the market or their cost becomes prohibitive.

If a terminal is not able to receive signaling information transmitted by all fixed stations, there is a risk that it will ask to connect (handover procedure) to a fixed station which will not guarantee best quality of communication available or when he requests this handover procedure when it was not necessary.

One solution to this problem would be to use two local oscillators, one used for the transmission and / or reception of traffic data, the other remaining stalled on the frequency at which signaling information is transmitted, a switching between the two local oscillators being carried out during the aforementioned guard or during the period during which the terminal neither receives nor transmits. The disadvantage of this solution is that it is expensive because each terminal must have two local oscillators.

The object of the present invention is in particular to remedy these disadvantages.

More specifically, one of the objectives of the invention is to provide a method ensuring that a terminal communicating in TDMA mode with a fixed station of such a cellular network can transmit or receive data from traffic while receiving in a predetermined period all the data from signaling transmitted by fixed stations.

This objective, as well as others which will appear later, is achieved thanks to a management method intended to allow the reception of information from signaling at a radio terminal communicating in TDMA mode with a fixed station, signaling information being transmitted by fixed stations in time intervals of a next and / or previous signaling frame traffic frames, the fixed stations being synchronized with each other, this process of changing the position of the signaling information with respect to that traffic data, issued or received by the terminal, so that the terminal can transmit or receive traffic data while receiving in a predetermined duration all the signaling information transmitted by the fixed stations.

The predetermined duration depends in particular on the rank of the time interval allocated to the terminal and the position change law used.

In one embodiment, changing the position of the signaling information compared to that of traffic data, transmitted or received by the terminal, consists in assigning to the terminal another time interval in the traffic frame.

In another embodiment, changing the position of the signaling information compared to that of traffic data, transmitted or received by the terminal, consists in changing the time intervals allocated to fixed stations for the transmission of signaling information.

• la figure 1 représente une multitrame transmise dans un réseau cellulaire du type considéré ;
• la figure 2 représente plus en détail les trames T24 et T25 de la multitrame de la figure 1 ;
• la figure 3 représente une opération de permutation circulaire des intervalles de temps réservés aux données de trafic ;
• la figure 4 représente une opération de permutation circulaire des intervalles de temps réservés aux informations de signalisation.

Other characteristics and advantages of the invention will appear on reading the following description of two preferred modes of implementation, given by way of illustration and not limitation, and of the appended drawings in which:

• FIG. 1 represents a multiframe transmitted in a cellular network of the type considered;
• Figure 2 shows in more detail the frames T24 and T25 of the multiframe of Figure 1;
• FIG. 3 represents a circular permutation operation of the time slots reserved for the traffic data;
• FIG. 4 represents a circular permutation operation of the time intervals reserved for the signaling information.

Figures 1 and 2 have been described above with reference to the state of the technical.

The principle of the invention lies in the fact that, to allow each terminal during communication to be able to receive information from signaling transmitted by the various fixed stations of the network, provision is made for change the position of the signaling information in relation to the traffic sent or received by each terminal. Change of position means a change in the time difference between two given time intervals frames T24 and T25 of FIG. 2 (and / or T25 and T26 and / or T50 and T51 and / or T51 and TO). The purpose of this modification is to increase in the more or less long term (in the aforementioned predetermined duration) this time difference, in order to leave a time sufficient for the local oscillator of the terminal to change its tuning frequency.

In a first embodiment, shown in FIG. 3, the change of position of signaling information in relation to data traffic, issued or received by the terminal, consists in assigning to this terminal another time interval in the traffic frame.

As a first example, the assignment to a terminal of another interval of time can is to perform a circular permutation of time intervals assigned to the different terminals. FIG. 3 represents this operation of circular permutation.

At time t0, corresponding to a time multiframe n, the frame T24 carries a maximum of 8 traffic data in time intervals IT0 to IT7. At time t1 ^- , corresponding to the next multiframe (or to the next half-multiframe, the frames T24 and T25 then in fact corresponding to the frames T50 and T51), a permutation of the time intervals is at the origin of the fact that the communication placed at the end of the frame, in the time interval IT7, is now placed at the start of the frame, in place of the time interval IT0. The terminal to which this time interval IT7 is allocated now no longer has the only guard time between T24 and T25 to change its tuning frequency in order to receive the signaling information of the frame T25, but more than 6 intervals of time. It is thus assured that this terminal will be able to "listen" to all the signaling information of the T25 frame. At the next time t2, the last time interval of the frame T24 will be IT5 and the first IT6, and so on.

For example, if only one circular permutation is performed by multiframe and that each terminal needs 4 time intervals to adjust its reception frequency, we are sure that each terminal will have been able to listen 4 times all traffic information transmitted after 8 permutations circular.

This assignment to a terminal of another time interval can also consist in reversing the order of the time intervals (passage of the sequence IT0 - IT1 - ... - IT6 - IT7 to sequence IT7 - IT6 - ... - IT1 - IT0) or provide any other arrangement of these time intervals to ensure in definitive that each terminal will have had access to all of the information signage. It is for example possible to use a pseudo-random jump law.

These operations correspond in fact to jumps of time intervals. Of same as for the frequencies used for the transmission of information from signaling, the frequencies used in the same frame for transmission traffic data are preferably identical. A jump law frequency may be provided to change the transmission frequencies at each frame of this traffic data.

In a second embodiment, shown in FIG. 4, the change of position of signaling information in relation to data traffic emitted or received by the terminal consists in changing the time intervals allocated to fixed stations for the transmission of signaling information.

In this implementation mode, instead of assigning another terminal to the terminal time slot in the traffic frame, these are the allocated time slots to fixed stations for the transmission of signaling information which is changed. In this example, as before, a circular permutation of time intervals is performed between times t0 and t1. This ensures that all terminals transmitting or receiving traffic data in T24 frames and T26 will have access within a specified time to all signaling information.

As before, other modes of changing intervals of times can be used (inversion of the order of time intervals, use of a pseudo-random sequence algorithm, ...).

Claims (3)

Management method intended to allow the reception of signaling information at the level of a radio terminal communicating in TDMA mode with a fixed station, said signaling information being transmitted by fixed stations in time intervals of a signaling frame following and / or preceding traffic frames, said fixed stations being synchronized with one another,
characterized in that it consists in changing the position of said signaling information with respect to that of said traffic data, transmitted or received by said terminal, so that said terminal can transmit or receive said traffic data while receiving in a predetermined duration all of said signaling information transmitted by said fixed stations. Method according to claim 1, characterized in that said change of the position of said signaling information relative to that of said traffic data, issued or received by said terminal, consists of assigning to said audit terminate another time slot in said traffic frame. Method according to claim 1, characterized in that said change of the position of said signaling information relative to that of said traffic data, issued or received by said terminal, consists of changing the time slots allocated to said fixed stations for the transmission of said signaling information.

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